Thread cutting mechanism in a sewing machine



8- 26, 1969 NORITOSHI AOYAMA 3,463,105

THREAD CUTTING MECHANISM IN A SEWING MACHINE Filed Nov. 5, 1967 6 Sheets-Sheet 2 m W 9. l I m (\J Q m K g 8 h N g 1N1 'ILVTOR.

MOI-U705!!! AOYAMA 8- 1969 NORITOSHI AOYAMA 3,463,105

THREAD CUTTING MECHANISM IN A SEWING MACHINE Filed Nov. 3, 1967 6 Sheets-Sheet 5 INVIZN T0 R NORBTOS I AOYAMA Aug. 26, 1969 NORITOSHI AQYAMA 3,463,105

THREAD CUTTING MECHANISM IN A SEWING MACHINE Filed Nov. 5, 1967 I e Sheeis-Sheet 4 IN VEN TOR. uomrosm AoYAMfl 1969 NORITOSHI AOYAMA 3,463,105

THREAD CUTTING MECHANISM IN A SEWING MACHINE Filed NOV. 5, 1967 6 Sheets-Sheet 5 NDRiTOSHi 9093/??? g- 1959 NORITOSHI AOYAMA 3,463,105

THREAD CUTTING MECHANISM IN A SEWING MACHINE Filed Nov. 5, 1967 s Sheets-Sheet e m- .maa'a'wllm IN VENTOR. mrggwni ADYAMR M,Am w @PM United States Patent Oifice 3,463,105 Patented Aug. 26, 1969 3,463,105 THREAD CUTTING MECHANISM IN A SEWING MACHINE Noritoshi Aoyama, Tokyo, Japan, assignor to Tokyo Juki Kogyo Kabushiki Kaisha, Tokyo, Japan Filed Nov. 3, 1967, Ser. No. 680,580 Claims priority, application Japan, Nov. 12, 1966,

Int. Cl. Db 65/00 US. Cl. 112-252 1 Claim ABSTRACT OF THE DISCLOSURE Thread cutting mechanism in a sewing machine which is adapted to be stopped at the end of stitching operation with the needle positioned at its lower dead point and with the portions of the upper thread from the needle as well as from the bobbin case after it travels around the bobbin case and the portion of the lower thread from the bobbin case forming together a knot within the cloth, and in which the needle is then retracted from the cloth and moved toward its upper dead point and stopped at a position adjacent to the upper dead point by the actuation in one direction of a lever swingably mounted on the machine, the combination of a connecting rod operatively coupled with said lever so that it is engaged with the bobbin case and disengaged therefrom, a lower knife operatively coupled with said lever and swingably located at the lower side of the needle plate adjacent to the needle hole, a fixed upper knife cooperating with said lower knife, and a link operatively coupled with said lever and being adapted to enter the space between the members of the thread tensioning disc and to be retracted therefrom, said lower knife being permitted to first effect the separation of the portion of the upper thread near the needle from the needle from the portion of the upper thread near the stitch in the cloth as well as the portion of the lower thread from the bobbin case during the movement of the lower knife in one direction in connection with the operation of said lever, said lower knife being thereafter caused to effect cutting of said portion of the upper thread near the stitch together with the portion of the lower thread from the bobbin case between said lower knife and said upper knife by the return movement of the lower knife.

BACKGROUND OF THE INVENTION The present invention relates to a thread cutting mechanism in a conventional sewing machine, and more particularly to a thread cutting mechanism in which the upper thread and the lower thread are simultaneously cut by driving the single and the same cutter means.

Heretofore, in the operation of a conventional Sewing machine, the ends of the upper thread and the lower thread extend from the upper surface and the lower surface of the cloth to be stitched to a fairly large extent at the beginning and the end of the stitching operation of the machine, and the ends of these threads are cut manually by using hand scissors in order to remove the waste portions of the threads.

However, such a manual operation for cutting the threads not only lowers the efiiciency of the sewing operation significantly, but also involves the danger that the cloth to be stitched might be damaged by the operation of the hand scissors.

SUMMARY OF THE INVENTION One object of the present invention is to provide a novel and improved thread cutting mechanism in a sewing machine which avoids the aforementioned difficulties.

Another object of the present invention is to provide a novel and improved thread cutting mechanism of the type described above which is simple in construction and easy in operation.

Another object of the present invention is to provide a novel and improved thread cutting mechanism of the type described above which can, by simple operation, cut the upper and lower threads extending from the cloth to be stitched at the end of the stitching operation by a short distance from the cloth from which they extend, thereby eliminating the troublesome manual operation of hand scissors for cutting the threads, so that the efiiciency of the sewing operation is increased and, at the same time, the danger of damaging the cloth by the hand scissors is avoided thereby resulting in improving the quality of the product and decreasing the amount of the waste thread used in sewing operation.

Other objects and advantages of the present invention will be clear by reading the following detailed description of a preferred embodiment of the present invention with reference to the accompanying drawings illustrating the embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of the preferred embodiment of the present invention with several parts shown in phantom line,

FIG. 2 is a schematic plan view showing the internal mechanism of the embodiment of the present invention located on the rear side of the bed plate of the sewing machine,

FIG. 3 is an enlarged cross-sectional view taken along line III-III in FIG. 1,

FIG. 4 is a cross-sectional view taken along line IV-IV' in FIG. 2,

FIG. 5 is a perspective view showing the bobbin of the lower thread before the thread is cut,

FIG. 6 is an exploded perspective view showing the parts constructing the thread cutting means of the present invention,

FIG. 7 is a fragmentary plan view of the needle plate as seen from the lower side thereof, each of the chaindot lines showing the movement of the lower cutter, and

FIGS. 8 and 9 are cross'sectional views taken along lines VIIIVIII' and IXIX' in FIG. 7, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring to the drawings, particularly to FIG. 1, a conventional sewing machine is illustrated in phantom line which includes bed 1, upright standard 2 extending upwardly from the upper surface of bed 1 and overhanging arm 4 integral at one end with the standard 2 and provided with head 3 at the extermity thereof. An elongated vertically extending lever 6 is freely swingably pivoted to the side of arm 4 adjacent to the upper portion of upright standard 2 by means of stepped machine screw 5. One end of connecting rod plate 8 is fixedly secured adjacent to the upper end of rod 6, the other end of said connecting rod plate 8 being operatively connected to a foot pedal (not shown) through chain 7. The lower end of lever 6 is coupled with one end of arm 13 through two spherical bearings 9, 10 and connecting rod 11 supporting said spherical bearings 9, 10, said arm 13 being fixedly secured at its other end to shaft 12 rotatably supported in bed 1 and extending downwardly, therethrough. One end of elongated link 14 is freely rotatably pivoted to the intermediate portion of lever 6 by means of stepped machine screw 15 secured to lever 6, the other end of said link 14 being rotatably connected to one end of L-shaped link member 17 by means of stepped machine screw 18 secured to link 14, said L-shaped link member 17 being freely rotatably pivoted to the side of head 3 by means of stepped machine screw 16. The other end of said L-shaped link 17 is provided with thread loosener 19 which is bent toward the outer side of head 3 so as to be located above thread tensioning disc 20 which is provided on the outer side of head 3. Bifurcated lever 23 is fixedly secured at the lower side of bed 1 to the lower end of shaft 12 which is rotatably fitted in the hole of bed 1 as shown in FIG. 2, stepped machine screws 21, 22 being secured to the respective arms of said bifurcated lever 23. One end of rod 24 is freely rotatably pivoted to one arm of lever 23 by means of said stepped machine screw 21, the other end of said lever 24 being rotatably connected by a stepped machine screw 21' to the right hand end of connecting rod 28 which is longitudinally shiftably mounted on the lower surface of bed 1 by means of two sets of bolt-slot means 28', 28". Connecting rod 28 is provided thereon with machine screws 25, 26 serving as spring holders, respectively, and projection 27. One end of spring 29 which is secured at its other end to the lower surface of bed 1 is held by said spring holder 25, thereby urging said connecting rod 28 toward the left in FIG. 2 by the action of said spring 29, so that shaft 12 is urged to be rotated anticlockwise together with bifurcated lever 23 through rod 24. Therefore, lever 6 is also urged to rotate clockwise as seen in FIG. 1 about said stepped machine screw through arm 13 and connecting rod 11. The rotation of lever 6 is limited by connecting rod 8 which is connected at the outer end to chain 7 which is in turn connected to the foot pedal not shown. The other end of said connecting rod 28 is bent in Z-shape as shown in FIGS. 2 and 5, the extremity of said bent end of connecting rod 28 being provided with jaw 30 which is positioned so as to engage with the lower portion of flange portion 32 of bobbin case 31. Rocking member 34 which is freely pivotably mounted on the lower surface of bed 1 by means of stepped machine screw 33 is provided with machine screw 35 serving as spring holder, projection 36 which is adapted to engage with spring holder 26 of connecting rod 28 and latching portion 37 which is adapted to engage with said projection 27 of connecting rod 28, while the other end of said rocking member 34 which is opposite to the end where said latching portion 37 is provided and is bent at right angle toward lower shaft 38 which is in turn coupled with the prime mover not shown and driven thereby is provided with roller 42 freely rotatably mounted thereon, said roller 42 being located adjacent to the outer peripheral surface of cam 41 fixedly secured to said lower shaft 38 and provided with projection 40 which is engageable with said roller 42. Spring holder 26 of connecting rod 28 and spring holder 35 of rocking member 34 hold respective ends of spring 43 so as to effect tension between rod 28 and rocking member 34, so that spring 43 urges rocking member 34 to rotate at all times clockwise about stepped machine screw 33. However, when connecting rod 28 is held in the left hand position shown by the solid line in FIG. 2, the rotation of said rocking member 34 is limited by the engagement of projection 36 of rocking member 34 with spring holder 26 of connecting rod 28, in this case latching portion 37 and roller 42 of rocking member 34 are held to be spaced apart from projection 27 of rod 28 and the outer peripheral surface of cam 41, respectively. When connecting rod 28 is shifted lengthwise to the right against the action of spring 29 as shown by chain-dot line in FIG. 2, spring holder 26 is disengaged from projection 36 of rocking member 34 thereby rotating rocking member 34 clockwise by the action of spring 43, thus permitting roller 42 of rocking member 34 to engage with the outer peripheral surface of cam 41 while latching portion 37 of rocking member 34 moves into engagement with projection 27 of connecting rod 28. One end of rod 44 is freely rotatably pivoted to the other arm of bifurcated lever 23 carrying stepped machine screw 22 by means of said stepped machine screw 22, the other end of said rod 44 being freely rotatably pivoted by means of stepped machine screw 22 to the right hand end of actuating rod 47 which is in turn freely rotatably pivoted to the lower surface of bed 1 by means of stepped machine screw 46. Actuating rod 47 is provided with latching portion 45 integral therewith and inverted L-shaped rocking piece which is freely pivotably mounted thereon. Pin 48 is fixedly secured adjacent to the outer end of one of the arms of said inverted L-shaped rocking piece 50, while the other arm of said L-shaped rocking piece 50 is bent at right angle toward lower shaft 38 and carries thereon roller 49 which is freely rotatably thereon and adapted to engage with the outer peripheral surface of cam 41 fixedly secured to lower shaft 38. Said cam 41 is provided with recess 39 engageable with said roller 49. Pin 48 of said L-shaped rocking piece 50 is loosely fitted in guide slot 53 formed in projection 52 of connecting rod 51 which is longitudinally shiftably mounted on the lower surface of bed 1 by means of two sets of pin-slot means 51'-51". Machine screw 54 serving as spring holder secured to said connecting rod 51 retains one end of spring 55, the other end of said spring 55 being secured to a fixed portion on the lower surface of bed 1. Connecting rod 51 is therefore urged toward the right in FIG. 2 by the action of spring 55. Thus, when actuating rod 47 is in the position shown by the solid line in FIG. 2, latching portion 45 of actuating rod 47 engages with projection 52 of connecting rod 51 thereby limiting the shifting movement of connecting rod 51 toward the right. In this case, roller 49 of rocking piece 50 is disengaged from the outer peripheral surface of cam 41 by virtue of the engagement of pin 48 secured to said rocking piece 50 with guide slot 53 in projection 52 of connecting rod 51. However, when actuating rod 47 is rotated anticlockwise about stepped machine screw 46 as shown by the two dot-chain lines in FIG. 2 so that latching portion 45 of actutaing rod 47 is disengaged from projection 52 of connecting rod 51, the latter is permitted to move lengthwise toward the right by the action of spring 55, thus rotating rocking piece 50 mounted on actuating rod 47 anticlockwise by the engagement of pin 48 with guide slot 53 of connecting rod 51, therefore, roller 49 of rocking piece 50 is engaged with the outer peripheral surface of cam 41 which, is provided with recess 39. A stud 56 is secured to connecting rod 51 at its outer end as shown in FIG. 6. This stud 56 extends loosely through elongated hole in bent portion 59 of a member 58 which is secured to the lower surface of bed 1 by means of stepped machine screws 57 passing through holes 57 in member 58 and secured to bed 1, respectively, as shown in FIGS. 6 and 7, and projects upwardly from said elongated hole 60. Said stud 56 also extends through a hole 63 provided in forked member 62 at its one end, said forked member 62 being pivotably mounted in said bent portion 59 of said member 58 by means of stepped machine screw 61 passing through hole 61 of member 62 and secured to hole 61" of member 58. Said forked member 62 is provided with bifurcation 64 at its other end. The surface of this bifurcation 64 is parallely offset upwardly in position from the surface of the body of said member 62. Member 58 pivotably mounts lower knife by means of securing pin 71 extending through hole 71 in member 58 and secured to hole 71" of lower knife 70. The tip end of said lower knife 70 is permitted to freely move across the lower end of needle hole 73 in needle plate 72. The cutting edge 68 of said lower knife 70 cooperates with cutting edge 65 of upper knife 65 which is secured to said member 58 by means of machine screws 65 passing through holes 65" in upper knife 65 and secured to holes 65" in member 58, so that the cutting of the threads is effected by the shearing action of the cutting edges. Lower knife 70 is formed with thread catching portion 67 at the side thereof opposite to the side where cutting edge 68 is provided as shown in FIG. 6. Lower knife 70 is also provided with pin 69 which loosely fits with said bifurcation 64 of forked member 62. Therefore, lower knife 70 is rotated about the axis of securing pin 71 by the engagement of said pin 69 with said bifurcation 64 of the forked member 62 as the latter is rotated by means of stud 56 as described hereinafter. The two dot-chain lines in FIG. 7 (VIII-VIII), FIG. 8 and FIG. 5 show the relative positions of thread catching portion 67, cutting edge 68 of lower knife 70 and cutting edge 66 of upper knife 65 with respect to the lower thread 76 extending from the cloth 74 to bobbin case 31 and the portion of the upper thread 78 which forms a loop together with the lower thread 76 and extends along the rear side surface of bobbin case 31 (right side in FIG. 5) toward needle 77 above cloth 74 and the portion of the upper thread 79 which is caught by jaw 30 of connecting rod 28 and extends along the front side surface of bobbin case 31 (left side in FIG. 5) toward cloth 74 to the stitched portion, wherein thread catching portion 67 of lower knife 70 urges the portion of the upper thread 78 outwardly away from the position where the cutting of threads is effected by the cutting edges while the portion of lower thread 76 and the portion of upper thread 79 are positioned between the cutting edge 66 of upper knife 65 and cutting edge 68 of lower knife 70 so that they are ready for being operated to cut the threads. The three dot-chain lines in FIG. 7 (IX-IX) and FIG. 9 shows the relative positions of upper and lower knives 65 and 70 with respect to the threads wherein the portion of the upper thread 79 and the portion of the lower thread 76 have been cut.

At the end of stitching operation of the machine of the present invention, needle 77 is stopped at a position adjacent to its lower dead point wherein the portions of the upper thread 78 and 79 and the portion of lower thread 76 from bobbin case 31 form together a knot within the cloth 74, and by the operation of lever 6 in one direction the machine is driven so that needle 77 is retracted from cloth 74 and the drive is stopped when the needle 77 reaches the position adjacent to the upper dead point thereof.

The sewing machine in accordance with the present invention is constructed as described above. The relative position of each element of the machine as shown by solid line in each of FIGS. 1, 2, 3 and 7 is such that stitching-operation for cloth 74 is continued or the upper and lower threads have been cut and the lever 6 is in its inoperative position. Therefore, in FIG. 2, shaft 12 is forced to rotate anticlockwise (clockwise in FIG. 3) by the action of spring 29 through connecting rod 28, rod 24 and arm 23 and, hence, lever 6 is forced to rotate clockwise (in FIG. 1) about the axis of stepped machine screw 5 and is arrested at a position determined by the limited position of connecting rod plate 8 fixed to said lever 6 at which point its upward movement is stopped by chain 7 connected to the pedal (not shown). Thread loosener 19 at one end of link 17 is located above the space between the two dish members constituting thread tension disc 20 by virtue of the connection of link 14 to said lever 6. And the forked member 62 and lower knife 70 are stopped at their positions shown by solid line in FIG. 7, since the connecting rod 52 is arrested at its right hand position as shown by solid line in FIG. 7. Since connecting rod 28 is arrested at its left hand position as shown bysolid line in FIG. 2, jaw 30 at the tip end of connecting rod 28 is positioned apart from flange portion 32 of bobbin case 31 as shown in FIG. 1.

In order to effect thread cutting by the machine of the present invention, the machine is first stopped by the automatic device for stopping the machine at the predetermined position wherein the portions of upper thread 78. and 79 and lower thread 76 form together a knot during the stitching operation, each of the elements of the machine being located \at its position as previously described 6. above. In the above described position of each of the elements of the machine, by depressing the pedal, lever 6 is rotated anticlockwise (FIG. 1) about the axis of stepped machine screw 5 against the action of spring 29 acting on rod 28 located on the lower surface of bed 1, and, at the same time, the machine is driven so that needle 77 is retracted from cloth 74 upwardly to the position adjacent to its upper dead point and stopped at the position.

By the rotation of lever 6 as described above, link 17 is rotated clockwise through link 14 about the axis of stepped machine screw 16, so that thread loosener 19 at one end of link 17 is projected into the space between the two dishes constituting thread tensioning disc 20 thereby releasing the clamping force of thread tensioning disc 20 which applies the predetermined tension to the upper thread, the releasing of the tension of the thread being so selected that it is effected beforeeach of the elements of the machine comes to the position shown in FIG. 5. The rotation of said lever 6 in anticlockwise direction also causes the rotation of shaft 12 in anticlockwise direction in FIG. 3 through two spherical bearings 9, 10 and connecting rod 11, and arm 23 secured to shaft 12 at the lower side of bed 1 is also rotated clockwise in FIG. 2 against the action of spring 29, thereby moving connecting rod 28 to the right in FIG. 2, thus resulting in the engagement of jaw 30 at the tip end thereof with flange portion 32 of bobbin case 31 as shown in FIG. 5. By the movement of said connecting rod 28 to the right in FIG. 2, propection 36 of rocking member 34 is released from the engagement with spring holder 26 of connecting rod 28, so that rocking member 34 is rotated clockwise by the action of spring 43, thereby resulting in engagement of latching portion 37 with prejection 27 of connecting rod 28, while roller 42 provided at the other end of rocking member 34 opposite to said latching portion 37 contacts with the outer peripheral surface of cam 41 fixedly secured to the lower shaft 38 which rotates during the drive of the machine. At the same time, actuating lever 47 is rotated anticlockwise about the axis of stepped machine screw 46 by the rotation of said arm 23 through rod 44, so that latching portion 45 of said actuating lever 47 is disengaged from projection 52 provided on connecting rod 51. Connecting rod 51 is thus moved to the right a short distance by the action of spring 55 so that rocking piece 50 is rotated anticlockwise through the engagement of pin 48 with slot 53, thereby permitting the contact of roller 49 with the outer peripheral surface of cam 41 secured to lower shaft 38, thus the rotation of rockingpiece 50 is controlled by the rotation of lower shaft 38 by virtue of the engagement of roller 49 of rocking piece 50 with said cam 41 secured to lower shaft 38. Subsequent rotation of lower shaft 38 causes the anticlockwise rotation of rocking piece 50 when roller 49 comes to the flatly cut portion 39 of cam 41, thereby moving connecting rod 51 to the right by virtue of the engagement ofpin 48 with guide slot 53 formed in connecting rod 51, so that forked member 62 and lower knife 70 are moved from their positions shown by solid line in FIG. 7 to their positions shown by the two dot-chain lines in FIG. 7. In other words, when connecting rod 51 moves from the position shown by solid line in FIG. 7 to the position shown by two dot-chain lines, forked member 62 is rotated anticlockwise about the axis of stepped machine screw 61 in FIG. 7 through stud 56 secured to the end of said connecting rod 51, thereby rotating lower knife 70 anticlockwise about the axis of pin 71 with pin 69 secured to lower knife 70 being slidingly guided along bifurcation 64- of forked member 62, so that said forked member 62 and said lower knife 70 are stopped at their positions shown by the two dot-chain lines in FIG. 7.

Link 17, jaw 30 and lower knife 70 which have been moved by the actuation of lever 6 act on the portions of upper and lower threads 78, 79 and 76 which have formed a knot within cloth 74 in such a manner as described below. The loop formed by the portion of upper thread 78 by the driving of the machine coupled with the actuation of lever 6 is first caught by jaw 30 adjacent to flange portion 32 of bobbin case 31 as shown in FIG. 5, and the portion of upper thread 78 is pulled upward by thread take-up lever (not shown), thereby requiring considerable amount of the thread to be supplied at a time; however, the thread loosener 19 of link 16 releases the clamping action to the upper thread 78 as described above thereby aiding the feed of the thread. The forked member 62 and lower knife 70 act against the portions of upper and lower thread 78, 79 and 76 located adjacent to the lower surface of needle plate 72 during the rotation of lower knife 70 in such a manner that thread catching portion 67 of lower knife 70 urges the portion of upper thread 78 located at the rear side of bobbin case 31 beneath the needle hole 73 of needle plate 72 outwardly, while the portion of upper thread 79 located at the front side of bobbin case 31 and the portion of lower thread 76 are moved to the position between cutting edge 66 of upper knife 65 secured to member 58 and cutting edge 68 of lower knife 70 as shown in FIGS. and 8, and they are stopped at their positions.

By the succeeding driving of the machine, rocking member 50 is rotated clockwise by virtue of roller 49 coming out of cam portion 39 of cam 41 which is rotated together with lower shaft 38, thereby moving connecting rod 51 to the left against the force of spring 55 through pin 48 loosely fitting in guide slot 53, so that forked member 62 and lower knife 70 are rotated reversely from the positions shown by two dot-chain lines in FIG. 7 to the positions shown by three dot-chain lines in FIGS. 7 and 9, thereby effecting the cutting of the portions of upper and lower threads 79 and 76 by the shearing action of cutting edge 66 of upper knife 65 and cutting edge 68 of lower knife 70 at the lower surface of needle plate 72 as shown in FIG. 9, and also rocking member 34 is rotated anticlockwise about the axis of stepped machine screw 33 against the force of spring 43 by virtue of roller 42 being engaged with projection 40 of cam 41 thereby disengaging projection 27 of connecting rod 28 from latching portion 37 of rocking member 34. Therefore, connecting rod 28 is moved to the left as shown in FIG. 2 by the action of spring 29, and hence, shaft 12 is rotated anticlockwise through rod 24, thereby rotating lever 6 clockwise in FIG. 1 about the axis of stepped machine screw 5 through arm 13, spherical bearings 9, and connecting rod 11 so that link 17, jaw 30 are moved in the reverse direction, opposite to that described above, while rocking member 34 is further rotated by the engagement of projection 36 of said rocking member 34 with spring holder 26 provided on connecting rod 28 during the movement of connecting rod 28 to the left. Thus, roller 42 is disengaged from cam 41. At the same time, actuating rod 47 is rotated clockwise about the axis of stepped machine screw 46 by the rotation of shaft 12 through rod 44 as shown by solid line in FIG. 2, thereby moving connecting rod 51 a short distance toward the left against the force of spring 55 through projection 52 of rod 51 which engages with latching portion 45 provided on actuating rod 47, so that the forked member 62 and lower knife 70 are moved from their positions shown by three dot-chain lines in FIG. 7 to the positions shown by solid line, while rocking member 50 is further rotated clockwise by the movement of connecting rod 51 toward the left through pin 48 of rocking member 50 which engages with guide slot 53 of rod 51 thereby disengaging roller 49 of rocking member '50 from cam 41, the drive of the machine then being stopped with each element of the machine returned and assuming the position as shown by solid line in FIGS. 1, 2, 3 and 7.

The present invention, as set forth hereinabove, provides a sewing machine in which knots are formed by the upper and lower threads within the cloth to be stitched and the needle is stopped at a position adjacent to the lower dead point thereof, and which is characterized by the features that, during the time the needle is withdrawn from the cloth by the driving of the sewing machine coupled with the actuation of the lever toward the upper dead point of the needle and stopped at a position adjacent thereto, the cutting operation of the upper and lower threads is made ready with the portions of the upper and lower threads adjacent to the stitches in the cloth being located between the cutting edges of the upper and lower knives provided at the lower side of the needle plate beneath the needle hole thereof, thereafter the portions of the upper and lower threads located between the cutting edges are cut simultaneously by the upper and lower knives by the return movement of the lower knife caused by the actuation of the cam secured to the lower shaft rotating during the driving of the machine, and each element of the machine is returned to the starting position prior to the next operation of the lever, thereby permitting the thread cutting mechanism to be held apart from the needle hole in the needle plate during the stitching operation of the machine so that accumulation of waste of the cloth and the thread adjacent to the position where the stitching is effected is avoided. Thus, the higher efficiency of thread cutting and positive cutting operation of the thread are assured. Since the threads are cut at the position adjacent to the lower surface of the needle plate, the threads extending from the cloth after they are cut can be made short, thereby dispensing with the troublesome manual operation of hand scissors for cutting the threads after the end of stitching operation as heretofore required in the prior art sewing machine. Therefore, the present invention assures high efficiency of the stitching operation of the sewing machine and also prevents the cloth to be stitched from being damaged during the stitching operation thereby improving the quality of the product. Further, since the rollers provided in the rocking members used in the mechanism are disengaged from the cooperating cams during the stitching operation, the driving of the machine is not disturbed by the movement of the rocking members and also the wear of contacting portions of the elements is kept to a minimum thereby assuring long working life.

The present invention thus provides a thread cutting mechanism of simple construction and easy operation.

I claim:

1. Thread cutting mechanism in a sewing machine which is adapted to be stopped at the end of stitching operation with the needle being held at a position adjacent to the lower dead point thereof and with the portion of the upper thread from the needle and the portion of the upper thread extending around the bobbin case from the cloth to be stitched and the portion of the lower thread from the bobbin case forming together a knot within the cloth, and in which the needle is then retracted from the cloth and moved toward the upper dead point thereof and stopped at a position adjacent to the upper dead point by the actuation in one direction of a lever swingably mounted on the machine, the improvement comprising the combination of a connecting rod which is operatively coupled with said lever so that it is engaged with the bobbin case and disengaged therefrom, a lower knife operatively coupled with said lever and swingably located at the lower side of the needle plate between the portion of the upper thread near the stitch in the cloth as well as the lower thread from the bobbin case and the portion of the upper thread near the needle, a fixed upper knife cooperating with said lower knife, and a link operatively coupled with said lever and being adapted to enter the space between the members constituting the thread tensioning disc and to be retracted therefrom, said lower knife being permitted to first effect the separation of the portion of the upper thread near the needle from the portion of the upper thread near the stitch in h 910th as well as the portion of the lower thread from 9 10 the bobbin case during the movement of the lower knife References Cited in one direction in connection with the operation of UNITED STATES PATENTS said lever, said lower knife being thereafter caused to 2,902,960 9/1959 Ketterer 5 effect the cutting of said portion of the upper thread 3,038,429 6/1962 Ketterer et a1. 112 -252 XR near the stitch together with the portion of the lower 5 3,139,849 7/ 964 Cohen et al. 112-252 thread from the bobbin case between said lower knife and said upper knife by the return movement of the lower knife. JAMES R. BOLER, Primary Examiner 

